1. Field of the Invention
The present invention relates to an image forming apparatus, and, more particularly, to an image forming apparatus having improved configuration of a paper supply device.
2. Description of the Related Art
An image forming apparatus is an apparatus to form an image on a printing medium. Examples of the image forming apparatus include, e.g., printers, copiers, facsimiles, and devices with some combination of functions of these.
An image forming apparatus includes a paper supply device to supply a printing medium (hereinafter, referred to as “paper” for convenience of description, but the present invention is not limited to paper) to a printing unit of the image forming apparatus.
The paper supply device includes a paper loading member, in which paper is loaded. The paper loading member generally takes the form of a cassette or a tray. The paper supply cassette can hold a plurality of sheets of paper therein, and is frequently used in an automatic paper supply mechanism. The paper supply tray conveniently supplies a sheet of paper or a special sheet of paper, and is frequently used as a manual paper supply mechanism.
FIG. 1 illustrates an example of an image forming apparatus having both a paper supply cassette and paper supply tray. As shown in FIG. 1, the image forming apparatus 1 includes a paper supply cassette 2 detachably mounted to a lower portion of a body 1a, and a paper supply tray 3 arranged above, and in parallel with, the paper supply cassette 2.
The paper supply tray 3 is arranged in the body 1a, and the body 1a has a paper input opening 4 through which a single sheet of paper can be placed on the paper supply tray 3.
The image forming apparatus 1 further includes a pickup roller 5 located above the paper supply cassette 2 and paper supply tray 3 and a pickup pad 6 disposed opposite the pickup roller 5 designed to prevent simultaneous delivery of two sheets of paper.
The pickup roller 5 is commonly used to pick up paper loaded in both the paper supply cassette 2 and paper supply tray 3. More specifically, when a printing operation is performed using the paper supply cassette 2 as shown in FIG. 1A, the pickup roller 5 picks up paper P1 loaded in the paper supply cassette 2 sheet by sheet. Also, when a printing operation is performed using a paper supply tray 3 as shown in FIG. 1B, the pickup roller 5 picks up paper P2 placed on the paper supply tray 3.
The above-described image forming apparatus 1 has an advantage of reducing the size of the apparatus as a result of arranging the paper supply cassette 2 and paper supply tray 3 in parallel. However, there is a risk that the paper loaded in the paper supply cassette 2 can be picked up by the pickup roller 5 even when it is intended to perform a printing operation using the paper supply tray 3, resulting in a simultaneous delivery of two sheets of paper.
For example, a printing operation using the paper supply cassette 2 frequently causes a situation, in which the paper P1 loaded in the paper supply cassette 2 is caught between the pickup roller 5 and the pickup pad 6 as shown in FIG. 1C. If the paper P2 is supplied from the paper supply tray 3 in this state, the paper P1 and paper P2 are picked up together by rotation of the pickup roller 5, thereby being delivered together.